Field
The present embodiments relate to a liquid crystal display device.
Related Art
Until recently, cathode-ray tubes (CRTs) have been typical used in display devices. Researchers are currently studying and developing various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays (FED), and electro-luminescence displays (ELDs), as a substitute for CRTs. These types of flat panel displays are driven in an active matrix type display, which has a plurality of pixels arranged in a matrix form. The plurality of pixels are driven using a plurality of thin film transistors therein. Among the active matrix types of flat panel displays, liquid crystal display (LCD) devices and electroluminescent display (ELD) devices are widely used for notebook computers and desktop computers because of their high resolution, ability to display colors and superiority in displaying moving images.
Conventionally, an LCD device includes two substrates that are spaced apart and face each other with a layer of liquid crystal molecules interposed between the two substrates. The two substrates include electrodes that face each other. A voltage applied between the electrodes induces an electric field across the layer of liquid crystal molecules. Alignment of the liquid crystal molecules changes in accordance with the intensity of the induced electric field in the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field across the layer of liquid crystal molecules.
As shown in FIG. 1, a liquid crystal panel 100 according to the related art includes a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm that cross each other to define a plurality of pixels P. Each pixel P includes a thin film transistor T, a liquid crystal capacitor Clc and a storage capacitor Cst. The liquid crystal capacitor Clc includes a pixel electrode, a common electrode and a liquid crystal layer between the pixel and common electrodes.
A data driver 110 supplies data voltages to the data lines DL1 to DLm. A gate driver 120 supplies gate voltages to the gate lines GL1 to GLn. A timing controller 130 supplies control signals to the data and gate drivers 110 and 120 and data signals to the data driver 110.
When an on gate voltage is applied to the gate line GL1 to GLn, the thin film transistor T connected to the gate line GL1 to GLn is turned on. When the thin film transistor T is turned on, the data voltage is applied to the pixel electrode of the pixel P through the data line DL1 to DLm and charged in the pixel P. A common voltage is applied to the common electrode. Accordingly, an electric field is induced to the liquid crystal and light transmissivity of the liquid crystal layer is changed, thereby displaying an image.
The liquid crystal has response delay. A pixel voltage charged in the pixel does not reach the data voltage applied, for example, a normal voltage displaying an image desired, during a charging period (frame period). Accordingly, the related art LCD device has problem of motion blurring.
Generally, an over driving method has been used to obviate the problem of motion blurring. The over driving method applies an over driving data voltage other than a data voltage corresponding to a data signal of a present frame. A data signal of the present frame is compared with a data signal of a previous frame. An over driving data voltage has a gray level higher than a data voltage of a data signal of the present frame when the data signal of the present frame has a gray level higher than the data signal of the previous frame. An over driving data voltage has a gray level lower than a data voltage of the data signal of the present frame when the data signal of the present frame has a gray level lower the data signal of the previous frame. Since the pixel is applied with the over driving data voltage higher or lower than the data voltage of the present frame, the response delay of the liquid crystal is compensated and a normal voltage desired to the pixel is reached in a frame period.
FIG. 2 is a waveform illustrating the over driving method of the related art LCD. FIG. 2(a) illustrates a pixel voltage charged in a pixel before adopting the over driving method, and FIG. 2(b) shows a pixel voltage charged in a pixel after adopting the over driving method.
As shown in FIG. 2(a), when the over driving method is not adopted, a data voltage 210, which is the same as a normal voltage, is applied to a pixel, and a pixel voltage charged in the pixel does not reach the normal voltage in a frame period Ts due to the response delay of the liquid crystal. As shown in FIG. 2(b), when the over driving method is adopted, an over driving data voltage 220, which is higher than the normal voltage, is applied to a pixel, and a pixel voltage charged in the pixel reaches the normal voltage in the frame period Ts.
When the data signal is an n-bit signal, 2n gray levels are displayed. Accordingly, the data driver use an n-bit data drive IC generating 2n gray level voltages corresponding to the 2n gray levels, for example, respectively.
When the LCD device having the n-bit data drive IC is operated in the over driving method, the 2n gray level voltages are also used for the over driving voltages.
When the n-bit data drive IC is used for the over driving method of the n-bit data signal, the over driving method can be performed for the middle gray levels.
For the highest gray level or the lowest gray level, for example, full bright gray level or full dark gray level, the over driving method can not be performed, because there is no over driving data voltages for the full bright or full dark gray level. For example, for the 9-bit data signal, 512 gray level voltages are generated. Since a 1st gray level or 512th gray level is a lowest or highest gray level, there is no over driving data voltages for the gray levels in the 512 gray level voltages. Accordingly, the over driving for the full bright or bull dark gray level can not be performed, and display quality is degraded.